This invention relates to a process for the torsionally resistant connection of a shaft to at least one part arranged on the shaft. In this process, the part is threaded with mating play onto the shaft and is fastened in a specific position on the latter by eliminating the mating play. The invention also relates to an assembly thus joined and to a camshaft thus joined.
It is known to fasten cams, for example, on shafts by shrink-fitting or by expanding the tubular shaft. For shrink-fitting (DE 33 01 749 A), a heated cam can be pushed onto the shaft and shrunk securely on the shaft by contracting during cooling. A tubular shaft can be expanded by applying appropriately high internal pressure to achieve frictionally engaging contact with the bores of cams arranged on the shaft (DE 38 03 687 A).
It has also already been proposed (DE 36 38 310 A) to use a shaft of a cross-sectionally unround outer contour, onto which the cams of correspondingly unround inner contours are fastened. The fastening of the cams on the polygonal shaft is intended to take place by interlocking actions of the polygon shape to be brought about by expanding the polygon faces or by compressing the polygon shoulders when pushing on the cams and the subsequent springing back of the polygonal tube.
Furthermore, it has already been proposed (DE 25 46 802 C) to provide the seating of the cams with an unround design and to deForm the wall of the tubular shaft into the unround seatings of the cams by generating high pressure in the space inside the shaft.
It has been found, however, that the frictional engagement which is required for the transmission of the forces occurring during operation of the shaft is not always achieved with the required reliability. Expansion of a tubular shaft by internal pressure requires considerable time to build up the very high pressure necessary, with the result that the cycle time for this method of production, and consequently its costs, are high.
It was therefore the object of the invention to provide a simple and inexpensive possible way of fastening parts such as cams, discs, gear wheels and the like securely on shafts, i.e. secured against torsion when maximum envisaged torques are applied. It achieves this object by the features stated in the characterizing clause of the main claim.
The unround profile, at least of the part to be fastened on the shaft, has the effect that the elimination of the mating play achieves virtually a keyed connection between the part and the shaft to the extent that the two parts oppose torsion with respect to each other with increasing resistance, the achieved final torque of which exceeds a torque to be transferred by the parts. The fact that the part is turned into the intended angular position after fastening on the shaft has the effect of increasing the frictional engagement to the value required for the torque to be transferred. A precondition for this is, of course, that the turning of the part to be fastened takes place in that direction in which the splines slide on one another. This turning into the intended position advantageously also takes place in that direction in which the part normally has to transfer torque during operation or--if transferring torques in both directions of rotation--the higher of two torques of different magnitudes.
The fact that the force required for turning a cam into the intended angular position on the shaft is measured additionally offers the possibility of testing, by comparison of the measured force with a setpoint value, whether the intended secure seating has been achieved. Since the turning into the intended angular position takes place at all the cams, the testing for achieving the desired secure seating is carried out at all the cams, thus the testing is not only 100% but is also non-destructive.
The effect according to the invention is already achieved if only the cam has the spline-surface profile. During shrink-fitting of the cam onto the shaft or during expansion of the shaft into the bore of the cam, the shaft is pressed into the profile shape of the cam. The keyed connection is particularly effective, however, if both the cam and the shaft have a matching spline-surface profile.
The cam can be shrink-fitted onto the shaft. Particularly advantageous, however, is a process in which the shaft is of a hollow design and is expanded into the bore of the cam. This expansion may take place by means of the known high-pressure internal expansion by means of pressure medium or by moving an expansion drift through the shaft.
Particularly effective fixing of the cam on the shaft takes place in this case if the expansion drift also has an adapted spline profile and is moved, preferably pulled, through the shaft in an angularly appropriate position, that is to say in a position in which it presses with its splines the splines of the shaft into the valleys between the splines of the cam.